Cold spraying method for coating compressor and turbine blade tips with abrasive materials

ABSTRACT

A method for coating compressor or turbine blade tips of a bladed disk with abrasive particles includes installing the blades onto a disk, and then cold gas-dynamic spraying the abrasive particles onto the blade tips while the blades are installed in the disk. According to another embodiment, a method for coating compressor and turbine blade tips of a bladed wheel with abrasive particles includes grinding the blade tips to bring the bladed wheel to a predetermined diameter. Then, surfaces of the bladed wheel not requiring coating are masked. After masking the surface not to be coated, the abrasive particles are cold gas-dynamic sprayed onto the blade tips. For both embodiments, an oxidation resistant layer may be cold gas-dynamic sprayed on the blade tips prior to spraying the abrasive particles.

FIELD OF THE INVENTION

The present invention generally relates to gas turbine engine componentsthat function in high pressure and elevated temperature environments.More particularly, the present invention relates to methods for coatingturbine engine components such as compressor or turbine blades toprevent or minimize wear during rubs with adjacent abradable shrouds.

BACKGROUND OF THE INVENTION

Turbine engines are used as the primary power source for various kindsof aircraft. The engines are also auxiliary power sources that drive aircompressors, hydraulic pumps, and industrial gas turbine (IGT) powergeneration. Further, the power from turbine engines is used forstationary power supplies such as backup electrical generators forhospitals and the like.

Most turbine engines generally follow the same basic power generationprocedure. Compressed air is mixed with fuel and burned, and theexpanding hot combustion gases are directed against stationary turbinevanes in the engine. The vanes turn the high velocity gas flow partiallysideways to impinge on the turbine blades mounted on a rotatable turbinedisk. The force of the impinging gas causes the turbine disk to spin athigh speed. Gas turbine engines use the power created by the rotatingturbine disk to power a bladed compressor that draws more air into theengine and to energize propellers, electrical generators, or otherdevices.

Since turbine engines provide power for many primary and secondaryfunctions, it is important to optimize the operating efficiency ofcompressors and turbines. One way to maximize compressor and turbineefficiency is to minimize high-pressure air leakage between the tips ofthe blades and the adjacent shroud. In order to accomplish thisobjective, compressor or turbine blade dimensions are tightly controlledand blade tips can be machined so the installed blades span a diameterthat is slightly smaller than the shroud inner diameter. Improvements incompressor or turbine performance are possible when compressor orturbine blade tips can tolerate interference rubs with the adjacentshroud without experiencing significant blade tip wear. Wear oftitanium, steel or superalloy blade tips during a rub is undesirablebecause clearances increase, producing an associated reduction incompressor or turbine performance.

In order to minimize the escape of high pressure air between compressorblade tips and the mating shroud, abrasive blade tip coatings may beapplied to machined compressor blades. Further, a porous and abradableceramic coating may be applied to the shroud as taught by Draskovich inU.S. Pat. No. 5,704,759. The primary function of such coatings is toprovide rub-tolerant shroud and blade surfaces that minimize bladedamage in the event a compressor blade rubs the surrounding shroudsurface. For example, U.S. Pat. No. 5,704,759 discloses a turbine bladebody having a tip portion that is coated with an abrasive material. Theabrasive material includes a dispersion of discrete particles of cubicboron nitride (CBN) that are formed on the blade tip by an entrapmentplating method wherein the CBN particles are entrapped in electroplatednickel with their tips (cutting edges) exposed. However, entrapmentplating is difficult to perform on large turbine components such as acompressor impeller. Furthermore, entrapment plating is a somewhatcumbersome process since each turbine blade must be individually coated.Because CBN is very hard and difficult to grind, each of the uncoatedblades must be inserted into slots in a hub. Then, the blades are groundat their outer diameters to conform to blue print dimension. Finally,the blades are removed from the hub and individually coated with CBN,and then reinserted into the slots in the hub. The steps ofdisassembling and reassembling the turbine wheel and its blades areburdensome and inefficient.

Entrapment electroplating of abrasive particles, such as CBN, into aco-deposited NiCoCrAlY matrix has also been applied to turbine bladetips as taught by Wride in U.S. Pat. No. 5,076,897. The hard CBNabrasive particles can cut into porous stabilized zirconia shroudcoatings for short periods of up to a few hours until the cubic boronnitride particles are lost due to oxidation.

Accordingly, it is desirable to provide turbine engine components suchas compressor and turbine blades that are coated and machined to preventair leakage between a gas turbine engine shroud and wheel blades. Inaddition, it is desirable to provide an efficient method for producingsuch components. Furthermore, other desirable features andcharacteristics of the present invention will become apparent from thesubsequent detailed description of the invention and the appendedclaims, taken in conjunction with the accompanying drawings and thisbackground of the invention.

BRIEF SUMMARY OF THE INVENTION

According to one embodiment of the invention, a method is provided forcoating compressor or turbine blade tips of a bladed disk with abrasiveparticles. The method includes installing the blades onto a disk, andthen cold gas-dynamic spraying the abrasive particles onto the bladetips while the blades are installed in the disk.

According to another embodiment of the invention, a method is providedfor coating compressor and turbine blade tips of a bladed wheel withabrasive particles. First, the blade tips are ground to bring the bladedwheel to a predetermined diameter. Then, surfaces of the bladed wheelnot requiring coating are masked. After masking the surface not to becoated, the abrasive particles are cold gas-dynamic sprayed onto theblade tips.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a perspective view of a blade for a turbine engine power wheelaccording to an embodiment of the invention;

FIG. 2 is a side view of a compressor blisk that is an integrally bladedrotor having a tip that is coated with cold sprayed abrasive particlesaccording to an embodiment of the invention;

FIG. 3 is a cross-sectional view depicting the tip of a compressor orturbine blade including a surface that is embedded with particles by acold gas-dynamic spraying process according to an embodiment of thepresent invention;

FIG. 4 is a cross-sectional view depicting the tip of a compressor orturbine blade including a thin oxidation resistant coating that isembedded with particles by a cold gas-dynamic spraying process accordingto an embodiment of the present invention;

FIG. 5 is a schematic view of an exemplary cold gas-dynamic sprayapparatus;

FIG. 6 is a side view of a gas turbine engine turbine wheel beside acold spraying nozzle that is spraying a turbine blade tip with abrasiveparticles according to an embodiment of the invention; and

FIG. 7 is a flow diagram of a coating method in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the invention or the applicationand uses of the invention. Furthermore, there is no intention to bebound by any theory presented in the preceding background of theinvention or the following detailed description of the invention.

The present invention includes methods for coating the machined tip ofany compressor or turbine blade. The methods are particularlyadvantageous when the compressor or turbine rotor is fully bladed andmachined. The rotor may be an integral bladed disk or a disk withinserted blades. When manufacturing a compressor or turbine wheel thatincorporates inserted compressor or turbine blades, the blades areinserted into slots in a disk.

Turning now to FIG. 1, an exemplary turbine blade 150 is illustrated.The turbine blade 150 is exemplary of the type of turbine blades thatare used in the turbine engines. Turbine blades commonly have adifferent shape, dimension and size depending on gas turbine enginemodels and applications. In a typical turbine engine, multiple turbineblades 150 are positioned in adjacent circumferential position along ahub or rotor disk. The turbine blades are typically made from advancedsuperalloys such as IN713, IN738, IN792, MarM247, GTD111, Rene142, ReneN5, SC180 and CMSX4 to name several non-exclusive examples.

The turbine blade 150 includes an airfoil 152. The airfoil 152 includesa concave curvature face and a convex face. In operation, hot gasesimpinge on the airfoil 152 concave face and thereby provide the drivingforce for the turbine engine. The airfoil 152 includes a leading edge162 and a trailing edge 164 that firstly and lastly encounter an airstream passing around airfoil 152. The blade 150 also includes a tip160. In some applications the tip may include raised features commonlyknown as squealers.

The turbine blade 150 is mounted on a turbine disk 146 that is part of awheel 20 depicted in FIG. 6. The blade 150 is attached to the disk 146by a fir tree or dovetail attachment 154 that extends downwardly fromthe airfoil 152 and engages a non-illustrated slot on the turbine hub146. A platform 156 extends longitudinally outwardly from the area wherethe airfoil 152 is joined to the attachment 154. A number of coolingchannels desirably extend through the interior of the airfoil 152,ending in openings 158 in the airfoil surface.

As previously discussed, the turbine blade 150 depicted in FIG. 1 isdesigned to be inserted into the wheel 20. However, turbine bladescommonly have different shapes, dimensions, and sizes depending on gasturbine engine models and applications. The present invention also isdirected to coating methods for compressor blades having an inserteddesign similar to that of the turbine blade 150. Furthermore, theturbine and compressor blades may be components of an integral bladeddisk. Turning now to FIG. 2, an exemplary integral compressor blisk 250is illustrated. In an exemplary turbine engine, multiple compressorblades 252 are circumferentially positioned adjacent to one anotheralong the outer surface of a hub 246. According to an exemplaryembodiment, compressor and impeller blades are made from titanium,steel, and superalloys, such as Ti-6A1-4V, M350, and IN718. Eachcompressor blade 252 includes an airfoil having a concave face and aconvex face. Each airfoil includes a leading edge 256 and a trailingedge 258 that firstly and lastly encounter an air stream passing aroundthe airfoil. Each blade 252 also includes a tip 254.

FIGS. 3 and 4 are a cross-sectional views depicting the tip of acompressor or turbine blade. The blade tip depicted in FIG. 3 includes asubstrate 10 and a surface 13 that is coated with particles 14 by a coldgas-dynamic spraying process. The substrate 10 may be formed fromvarious metals such as steel alloys, structural aluminum alloys,titanium alloys such as Ti-6A1-4V, and superalloys such as anickel-based superalloy IN718, MarM247 or SC180. According to anexemplary embodiment, the substrate 10 is sufficiently oxidationresistant to provide the surface 13 into which a single layer or aplurality of layers of particles 14 is partially imbedded by highvelocity impaction during cold gas-dynamic spraying. The substrate 10for the blade tip depicted in FIG. 4 has a thin oxidation resistantmetallic coating 12 that formed thereon, and the coating 12 has asurface 15 into which a single layer of particles 14 are partiallyimbedded by high velocity impaction during cold gas-dynamic spraying.The cold gas-dynamic spraying process includes accelerating the abrasiveparticles at a velocity that is sufficient for the particles to beembedded into the surface. However, the abrasive particles are onlypartially embedded so the abrasive particles protrude above the metallicsubstrate 10 or the coating 12.

According to an exemplary embodiment, the abrasive particles are cubicboron nitride (CBN). The CBN preferably has an average particle diameterranging between 25 and 100 microns. Other abrasive materials may also besuitably applied by a cold gas-dynamic spraying process. Some exemplaryabrasive materials include diamond, silicon carbide (SiC), yttriumaluminum garnet (YAG), and cubic zirconia. Diamond and CBN are harderthan SiC, YAG and cubic zirconia. However, these and other suitableabrasive materials may be selected based on their high temperatureoxidation resistance properties. The abrasive coating composition alsomay vary depending on the type of blades that are being coated and theintended operational conditions for the blades.

As previously discussed, a single layer of abrasive particles 14 areimbedded into compressor and turbine blade tips using a cold gas-dynamicspraying process which accelerates the particles to supersonicvelocities. Turning now to FIG. 5, an exemplary cold gas-dynamic spraysystem 100 is illustrated diagrammatically. The system 100 isillustrated as a general scheme, and additional features and componentscan be implemented into the system 100 as necessary. The main componentsof the cold-gas-dynamic spray system 100 include a powder feeder forproviding abrasive powder, a carrier gas supply (typically including aheater) for heating and accelerating powder particles, a mixing chamberand a nozzle. In general, the system 100 transports the abrasive powderwith a suitable pressurized gas to the mixing chamber. The particles areaccelerated by the pressurized carrier gas, such as air, helium,nitrogen, or mixtures thereof, through the specially designed nozzle anddirected toward a targeted surface on the turbine component. When theparticles strike the target surface, converted kinetic energy of theparticle causes plastic deformation in the target metallic substrate(the blade tip surface), which permits the particles to partially embedthe surface. Thus, the cold gas-dynamic spray system 100 can bond thepowder materials to a turbine blade tip surface and thereby form aprotective coating on the tip.

The cold gas dynamic spray process is referred to as a “cold spray”process because the particles are applied at a temperature that is wellbelow their melting point. The kinetic energy of the particles on impactwith the target surface, rather than particle temperature, causes thesubstrate to plastically deform and bond the particles with the targetsurface.

A variety of different systems and implementations can be used toperform the cold gas-dynamic spraying process. For example, U.S. Pat.No. 5,302,414, entitled “Gas-Dynamic Spraying Method for Applying aCoating” describes an apparatus designed to accelerate materials and tomix particles of the materials with a process gas to provide theparticles with a density of mass flow between 0.05 and 17 g/s·cm².Supersonic velocity is imparted to the gas flow, with the jet formed athigh density and low temperature using a predetermined profile. Theresulting gas and powder mixture is introduced into the supersonic jetto impart sufficient acceleration to ensure a particle velocity rangingbetween 300 and 1200 m/s.

According to the present invention, the cold gas-dynamic spray system100 applies abrasive particles onto a compressor or a turbine blade tip.Although the process is referred to as “cold spraying,” some warming ofthe gas and/or particles may be advantageous in order to provide theabrasive particles with sufficient energy to embed into a turbine bladetip. The system typically uses gas pressures of between 5 and 20 atm,and at a temperature ranging between about 300 and 1000° F. Furthermore,the abrasive particles may be warmed to a temperature of up to about500° F. However, any warming of the particles and/or the propellant gasis tailored to maintain the particle temperatures well below theirmelting points. As non limiting examples, the gases can comprise air,nitrogen, helium and mixtures thereof. Again, this system is but oneexample of the type of system that can be adapted to cold spray powdermaterials to the target surface. The system 100 is typically operable inan ambient external environment.

A unique advantage provided by cold gas-dynamic spraying abrasiveparticles is the ability to deposit the abrasives onto the tips ofblades that are installed on a disk. As previously discussed, manyconventional methods of coating compressor and turbine blades withabrasives are somewhat cumbersome processes since the methods requirethat each turbine blade be individually coated. Because CBN and othersuitable abrasives are very hard and difficult to grind, each of theuncoated blades are inserted into slots in a disk using conventionalmethods, and the blades are then ground at their outer diameters toconform to the bladed disk's blue print dimension. The blades arethereafter removed from the disk and individually coated with theabrasive material, and then reinserted into the slots in the disk. Thesteps of disassembling and reassembling the turbine wheel and its bladesare burdensome and inefficient. Returning now to FIG. 6, a side view isdepicted of the gas turbine engine bladed disk 20 beside a cold sprayingnozzle 34 that is spraying a compressor or turbine blade tip 160 withabrasive particles according to an embodiment of the invention. Becausethe blades are inserted into the hub during deposition of the abrasiveparticles, the disassembling and reassembling steps from theconventional process are eliminated. Sheet metal or rubber masking (notshown) protects the other non-blade tip surfaces of the bladed disk fromdeposition of the abrasive powder. Only the blade tip surfaces areexposed to the high-velocity flux of abrasive coating powder.

According to the embodiment depicted in FIG. 6, the cold sprayingapparatus 100 includes the nozzle 34 that is communicatively coupled toa propellant gas heater 32 by way of a main gas passage 36. A premixchamber 38 is in line with the main gas passage 36 upstream of thenozzle 34, and is upstream of the nozzle 34. The gas is transferred fromthe premix chamber 38 into a mixing chamber 40 where the gas is combinedwith the abrasive particles and any other metal powders. The particlesare transferred to the mixing chamber 40 using an injection tube 50 thatis in communication with a powder feeder that supplies the particles.The gas-dynamic spraying is enabled by using a nozzle that includes athroat 58 or other aperture that is sized to optimize the gas pressureand, in turn, the particle velocity as it passes through the nozzle 34.

Turning now to FIG. 7, a flow diagram outlines an exemplary coatingmethod in accordance with an embodiment of the invention. As step 60, abladed wheel having an inserted blade design is assembled by installingthe compressor or turbine blades onto the disk. The hub includes slotsthat are sized to receive and secure the blades. An exemplary blade isattached to the hub by a dovetail that extends downwardly from theblade's airfoil and engages the slot on the hub. As previouslydiscussed, according to another embodiment a compressor or turbine bliskhaving an integrally bladed rotor is used. According to such anembodiment, no assembly of the blades into a disk is performed.

With the blades installed on the hub, the blade tips are ground topredetermined or blueprint dimensions as step 62. During operation of agas turbine engine, the turbine wheel blades are surrounded by a shroud.Engine power and operational efficiency are optimized by forming thecompressor or turbine wheel to have a diameter that minimizes the bladetip to shroud clearance, which prevents wasteful high pressure airleakage between the blades and the shroud.

As step 64, a protective mask is applied to protect surfaces of thebladed disk where the deposition of abrasive particles is not permitted.The protective mask may include strips of rubber or sheet metal withairfoil shaped slots to expose the tips of the blades.

As step 66, the tips of the installed compressor or turbine blades arecoated with abrasive particles by a cold gas-dynamic spraying process.According to the exemplary embodiment depicted in FIG. 6, the tips aresprayed by positioning the spraying nozzle radially in line with, anddirectly opposing, the blade tips so the abrasive particles are sprayedsubstantially normal to the blade tip surface. However, other nozzlepositions with respect to the blade tips may be employed to ensureadequate blade tip coating. A mask that leaves the blade tips exposedbut covers or otherwise shields the remainder of the wheel may beemployed when spraying the abrasive particles. According to oneembodiment, the abrasives are constantly sprayed toward the blade tipswhile the turbine wheel is continuously spun. According to anotherembodiment, spinning of the wheel is intermittently halted when eachindividual blade reaches a position to receive a coating of abrasivematerials. Spraying may also be intermittent in order to avoid waste ofabrasive material when the blade tips are not aligned with the sprayingnozzle. In order to further increase manufacturing efficiency, the hubmay be installed on a shaft 144, depicted in FIG. 6, while coldgas-dynamic spraying the abrasive materials onto the turbine blade tips.

As necessary or useful, an optional heat treatment may be performed asstep 68 after cold gas-dynamic spraying the abrasive particles onto theturbine blade tips and before installing the compressor or turbine wheelinto an engine. A heat treatment may improve metallurgical bondingbetween the abrasive particles and the turbine blade material.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It is understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims.

1. A method for coating compressor or turbine blade tips of a bladeddisk with abrasive particles, comprising the steps of: installing theblades onto a disk; and cold gas-dynamic spraying the abrasive particlesonto the blade tips while the blades are installed in the disk.
 2. Themethod according to claim 1, further comprising the step of: grindingthe blade tips, after installing the blades onto the disk and beforecold gas-dynamic spraying the abrasive particles onto the blade tips,until the bladed disk is brought to a predetermined diameter.
 3. Themethod according to claim 1, further comprising the step of: maskingsurfaces of the bladed disk not requiring the abrasive coating beforeperforming the cold gas-dynamic spraying step.
 4. The method accordingto claim 1, wherein the method excludes any grinding of the blade tipsafter cold gas-dynamic spraying the abrasive particles.
 5. The methodaccording to claim 1, further comprising the step of: heat treating theblade tips after cold gas-dynamic spraying the abrasive particles. 6.The method according to claim 1, wherein the method excludes removing ofthe turbine blades from the disk after cold gas-dynamic spraying theabrasive particles.
 7. The method according to claim 1, wherein the stepof cold gas-dynamic spraying the abrasive particles onto blade tipscomprises spraying abrasive particles selected from the group consistingof cubic boron nitride, diamond, silicon carbide, yttrium aluminumgarnet, and cubic zirconia.
 8. The method according to claim 7, whereinthe step of cold gas-dynamic spraying the abrasive particles onto theblade tips comprises spraying cubic boron nitride particles.
 9. Themethod according to claim 7, wherein the step of cold gas-dynamicspraying the abrasive particles onto the blade tips comprises sprayingparticles having an average diameter ranging between 25 and 100 microns.10. The method according to claim 8, further comprising the step of:forming a MCrAlY oxidation resistant layer on the blade tips prior tocold gas-dynamic spraying the abrasive particles. 11 The methodaccording to claim 10, wherein the MCrAlY oxidation resistant layer isformed using a cold gas-dynamic spraying process.
 12. The methodaccording to claim 1, wherein the step of cold gas-dynamic spraying theabrasive particles onto the turbine blades comprises partially embeddingthe particles into the tips of the blades.
 13. The method according toclaim 1, wherein the step of cold gas-dynamic spraying the abrasiveparticles onto the turbine blades comprises spraying only tip portionsof the blades with the abrasive particles.
 14. The method according toclaim 1, wherein the step of cold gas-dynamic spraying the abrasiveparticles onto the turbine blades comprises the step of spraying theabrasive particles while spinning the bladed disk.
 15. The methodaccording to claim 14, wherein the step of spraying the abrasiveparticles while spinning the bladed disk comprises constantly sprayingthe abrasive particles until each blade tip is coated with the abrasiveparticles.
 16. The method according to claim 14, spraying the abrasiveparticles while spinning the bladed disk comprises intermittentlyhalting the spinning when each individual blade reaches a position toreceive a coating of abrasive materials.
 17. A method for coatingcompressor and turbine blade tips of an integrally bladed wheel withabrasive particles, comprising the steps of: grinding the blade tips tobring the bladed wheel to a predetermined diameter; masking surfaces ofthe bladed wheel not requiring coating; and cold gas-dynamic sprayingthe abrasive particles onto the blade tips.
 18. The method according toclaim 17, wherein the bladed wheel is selected from the group consistingof an integral axial compressor wheel, an impeller, and an integralturbine wheel.
 19. The method according to claim 17, wherein the step ofcold gas-dynamic spraying the abrasive particles onto the turbine bladescomprises the step of spraying the abrasive particles while spinning thebladed disk.
 20. The method according to claim 19, wherein the step ofspraying the abrasive particles while spinning the bladed disk comprisesconstantly spraying the abrasive particles until each blade tip iscoated with the abrasive particles.
 21. The method according to claim19, wherein the step of spraying the abrasive particles while spinningthe bladed disk comprises intermittently halting the spinning when eachindividual blade reaches a position to receive a coating of abrasivematerials.